// Problem: 
// Contest: 
// URL: 
// Memory Limit: 
// Time Limit: 
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#include<bits/stdc++.h>
using namespace std;
#define int long long
inline int read(){
	int s=0,w=1;
	char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') s=s*10+ch-'0',ch=getchar();
	return s*w;
}
struct node
{
	int p,c;
};
signed main()
{
	int t=1;
//	cin>>t;
	while(t--)
	{
		int n,s,sum=0,ans=0,ssum=0;
		cin>>n>>s;
		vector<node> v(n+1);
		vector<int> w(1e6);
		for(int i=1;i<=n;i++)
		{
			cin>>v[i].p>>v[i].c;
			w[v[i].c]+=v[i].p;
			sum+=v[i].p;
			ssum+=v[i].p*v[i].c;
		}
		for(int i=1;i<=1e6;i++)
		{
			if(sum<s)break;
			ans+=s;
			ssum-=sum;
			sum-=w[i];	
		}
		ans+=ssum;
		cout<<ans;
	}
	return 0;
}
